JP2015157547A - pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress occurrence of a crack generated on an interface of a cap tread rubber layer and reduce electric resistance values.SOLUTION: A pneumatic tire has at a tread part 2: a cap tread rubber layer 2A having at least two kinds of rubber compositions 2Aa and 2Ab provided on a surface of the tread part in a tire width direction; an under tread rubber layer 2B provided inside in a tire radial direction of the cap tread rubber layer; and cord reinforcing layers 8 and 7 provided inside in the tire radial direction of the under tread rubber layer, in which a main groove 22 is formed that extends along a tire circumference direction so as to have a boundary between the respective rubber compositions of the cap tread rubber layer as a groove bottom. Further, the tire comprises a conductive rubber layer 10 that has: a groove surface part 10a covering a groove surface of the main groove; and a groove-bottom extending part 10b that extends inside in the tire radial direction of the groove bottom of the main groove from the groove surface part at the boundary of the respective rubber compositions of the cap tread rubber layer, penetrates through the under tread rubber layer and contacts the cord reinforcing layer.

Description

  The present invention is a pneumatic tire in which at least two types of cap tread rubber layers are arranged in the tire width direction, suppresses the occurrence of cracks starting from the interface of the cap tread rubber layers, and reduces the electrical resistance value. Related to pneumatic tires.

  For example, in a pneumatic tire that is mounted on a vehicle that is assumed to be traveling at high speed, in order to achieve both steering stability on a dry road surface and steering stability on a wet road surface, rubber is provided in different areas in the tire width direction of the tread portion. A dual tread structure in which two types of cap tread rubber layers having different compositions are arranged is employed.

  In a pneumatic tire having such a dual tread structure, if there is an interface of the cap tread rubber layer on the tread surface, step wear may occur at the interface, or chipping or tread starting from the interface may occur. There is a risk of peeling. Therefore, conventionally, in a pneumatic tire in which at least two types of cap tread rubber layers having different rubber compositions are arranged in different regions in the tire width direction of the tread portion, the interface of these cap tread rubber layers is arranged in the tire circumferential direction at the tread portion. It is known that a reinforcing rubber layer that is disposed under the extending main groove and has a breaking strength of 15 MPa or more and a breaking elongation of 550% or more is interposed at least at the interface of the cap tread rubber layer (for example, Patent Document 1). reference).

JP 2009-126314 A

  The pneumatic tire disclosed in Patent Document 1 described above suppresses the occurrence of cracks (groove cracks) starting from the interface of the cap tread rubber layer in the pneumatic tire in which at least two types of cap tread rubber layers are arranged in the tire width direction. Is possible.

In the pneumatic tire disclosed in Patent Document 1, an undertread rubber layer is embedded in a tread portion, the reinforcing rubber layer is disposed so as to contact the undertread rubber layer, and the electric resistance of the reinforcing rubber layer is 10 ^8. By configuring the conductive rubber composition to be Ω · cm or less, the electric resistance value is reduced. However, in recent years, further reduction in electrical resistance is desired.

  The present invention has been made in view of the above, and in the configuration in which at least two kinds of cap tread rubber layers are arranged in the tire width direction, the occurrence of cracks starting from the interface of the cap tread rubber layer is suppressed, And it aims at providing the pneumatic tire which can reduce an electrical resistance value.

  In order to solve the above-described problems and achieve the object, the pneumatic tire of the present invention includes a cap having at least two types of rubber compositions provided in the tread portion in the tire width direction on the surface of the tread portion. A tread rubber layer; an under tread rubber layer provided on the inner side in the tire radial direction of the cap tread rubber layer; and a cord reinforcing layer provided on the inner side in the tire radial direction of the under tread rubber layer; In the pneumatic tire in which the main groove extending along the tire circumferential direction is formed so that the boundary of each rubber composition of the tread rubber layer is the groove bottom, a groove surface portion covering the groove surface of the main groove; The cap tread rubber layer extends from the groove surface portion at the boundary of each rubber composition to the inside in the tire radial direction of the groove bottom of the main groove and penetrates the under tread rubber layer. Characterized in that it comprises a conductive rubber layer having a groove bottom extending portion which contacts the over-de reinforcing layer.

  According to this pneumatic tire, since the boundary of each rubber composition of the cap tread rubber layer is arranged at the groove bottom position of the main groove, the boundary does not contact the road surface. Occurrence can be prevented. Moreover, according to this pneumatic tire, by providing the conductive rubber layer in which the groove surface of the main groove is covered with the groove surface portion and the groove bottom extending portion is disposed at the boundary position, the boundary of each rubber composition is provided. It is possible to suppress the occurrence of cracks starting from. Furthermore, according to this pneumatic tire, since the groove bottom extension portion penetrates the undertread rubber layer and comes into contact with the cord reinforcing layer, the electric resistance value can be reduced.

  In the pneumatic tire of the present invention, the conductive rubber layer has a breaking strength of 15 MPa or more and a breaking elongation of 550% or more.

  According to this pneumatic tire, the effect of suppressing the occurrence of cracks starting from the boundaries of the respective rubber compositions can be significantly obtained by the breaking strength and breaking elongation set in the conductive rubber layer.

In the pneumatic tire of the present invention, the conductive rubber layer has an electric resistance value of 10 ⁶ Ω · cm or less.

  According to this pneumatic tire, the effect of reducing the electrical resistance value can be remarkably obtained by the electrical resistance value set in the conductive rubber layer.

  In the pneumatic tire of the present invention, the conductive rubber layer has a thickness in a tire meridian cross section of not less than 0.5 mm and not more than 6.0 mm.

  According to this pneumatic tire, when the thickness of the conductive rubber layer is 0.5 mm or more, the effect of reducing electrical resistance is increased, and when the thickness is 6.0 mm or less, the volume of the conductive rubber layer increases and the vehicle travels. High-speed durability due to heat generation can be ensured.

  In the pneumatic tire of the present invention, the difference in hardness of the conductive rubber layer is ± 5 pt with respect to the hardness of each cap tread rubber layer on both sides in the tire width direction with the conductive rubber layer as a boundary. Features.

  According to this pneumatic tire, if the hardness difference of the conductive rubber layer with respect to the cap tread rubber layer is ± 5 pt, the peeling force between the cap tread rubber layer and the conductive rubber layer can be suppressed to a small level. High speed durability can be ensured.

  Further, in the pneumatic tire of the present invention, the conductive rubber layer is formed such that a thickness of the groove bottom extension portion in a tire meridian section is thicker than a thickness of the groove surface portion. To do.

  According to this pneumatic tire, conductivity to the cord reinforcing layer can be ensured.

  Further, in the pneumatic tire of the present invention, the conductive rubber layer is characterized in that the shape of the groove bottom extending portion in the tire meridional section is formed to gradually increase in thickness toward the inner side in the tire radial direction. To do.

  According to this pneumatic tire, conductivity to the cord reinforcing layer can be ensured.

  In the pneumatic tire according to the present invention, in the configuration in which at least two types of cap tread rubber layers are arranged in the tire width direction, the occurrence of cracks starting from the interface of the cap tread rubber layer is suppressed, and the electrical resistance value is reduced. can do.

FIG. 1 is a meridional sectional view of a pneumatic tire according to an embodiment of the present invention. FIG. 2 is an enlarged view of a main part of the pneumatic tire according to the embodiment of the present invention. FIG. 3 is an enlarged view of a main part of the pneumatic tire according to the embodiment of the present invention. FIG. 4 is an enlarged view of a main part of the pneumatic tire according to the embodiment of the present invention. FIG. 5 is an enlarged view of a main part of the pneumatic tire according to the embodiment of the present invention. FIG. 6 is a chart showing the results of the performance test of the pneumatic tire according to the example of the present invention.

  Embodiments of the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by this embodiment. The constituent elements of this embodiment include those that can be easily replaced by those skilled in the art or those that are substantially the same. Further, a plurality of modifications described in this embodiment can be arbitrarily combined within the scope obvious to those skilled in the art.

  FIG. 1 is a meridional sectional view of a pneumatic tire according to this embodiment.

  In the following description, the tire radial direction refers to a direction orthogonal to the rotation axis (not shown) of the pneumatic tire 1, and the tire radial direction inner side refers to the side toward the rotation axis in the tire radial direction, the tire radial direction outer side. Means the side away from the rotation axis in the tire radial direction. Further, the tire circumferential direction refers to a direction around the rotation axis as a central axis. Further, the tire width direction means a direction parallel to the rotation axis, the inner side in the tire width direction means the side toward the tire equator plane (tire equator line) CL in the tire width direction, and the outer side in the tire width direction means the tire width direction. Is the side away from the tire equatorial plane CL. The tire equatorial plane CL is a plane that is orthogonal to the rotation axis of the pneumatic tire 1 and passes through the center of the tire width of the pneumatic tire 1. The tire width is the width in the tire width direction between the portions located outside in the tire width direction, that is, the distance between the portions farthest from the tire equatorial plane CL in the tire width direction. The tire equator line is a line along the tire circumferential direction of the pneumatic tire 1 on the tire equator plane CL. In the present embodiment, the same sign “CL” as that of the tire equator plane is attached to the tire equator line.

  As shown in FIG. 1, the pneumatic tire 1 according to the present embodiment includes a tread portion 2, shoulder portions 3 on both sides thereof, and a sidewall portion 4 and a bead portion 5 that are sequentially continuous from the shoulder portions 3. ing. The pneumatic tire 1 includes a carcass layer 6, a belt layer 7, a belt reinforcing layer 8, and an inner liner layer 9.

  The tread portion 2 is made of tread rubber, is exposed at the outermost side in the tire radial direction of the pneumatic tire 1, and the surface thereof is the contour of the pneumatic tire 1. A tread surface 21 is formed on the outer peripheral surface of the tread portion 2, that is, on the tread surface that contacts the road surface during traveling. The tread surface 21 is provided with a plurality of (four in this embodiment) main grooves 22 which are straight main grooves extending along the tire circumferential direction and parallel to the tire equator line CL. The tread surface 21 is formed with a plurality of rib-like land portions 23 extending along the tire circumferential direction by the plurality of main grooves 22. The main groove 22 may be formed to be bent or curved while extending along the tire circumferential direction. The tread surface 21 is provided with a lug groove 24 extending in a direction intersecting the main groove 22 in the land portion 23. In the present embodiment, the lug groove 24 is shown in the outermost land portion 23 in the tire width direction. The lug groove 24 may intersect the main groove 22, or at least one end of the lug groove 24 may not terminate the main groove 22 and terminate in the land portion 23. When both ends of the lug groove 24 intersect with the main groove 22, a block-shaped land portion in which the land portion 23 is divided into a plurality of portions in the tire circumferential direction is formed. Note that the lug groove 24 may be formed to be bent or curved while extending while being inclined with respect to the tire circumferential direction.

  The shoulder portion 3 is a portion on both outer sides in the tire width direction of the tread portion 2. Further, the sidewall portion 4 is exposed at the outermost side in the tire width direction of the pneumatic tire 1. The bead unit 5 includes a bead core 51 and a bead filler 52. The bead core 51 is formed by winding a bead wire, which is a steel wire, in a ring shape. The bead filler 52 is a rubber material disposed in a space formed by folding the end portion in the tire width direction of the carcass layer 6 at the position of the bead core 51.

  The carcass layer 6 is configured such that each tire width direction end portion is folded back from the tire width direction inner side to the tire width direction outer side by a pair of bead cores 51 and is wound around in a toroidal shape in the tire circumferential direction. It is. The carcass layer 6 is formed by coating a plurality of carcass cords (not shown) arranged in parallel at an angle in the tire circumferential direction with an angle with respect to the tire circumferential direction being along the tire meridian direction. The carcass cord is made of organic fibers (polyester, rayon, nylon, etc.). The carcass layer 6 is provided as at least one layer. In FIG. 1, the carcass layer 6 is provided such that the folded end covers the tire width direction end of the belt layer 7, but the folded end may not reach the belt layer 7. Good.

  The belt layer 7 is configured as a cord reinforcing layer in the present embodiment. The belt layer 7 has a multilayer structure in which at least two belts 71 and 72 are laminated, and is disposed on the outer side in the tire radial direction which is the outer periphery of the carcass layer 6 in the tread portion 2 and covers the carcass layer 6 in the tire circumferential direction. It is. The belts 71 and 72 are made by coating a plurality of cords (not shown) arranged in parallel at a predetermined angle (for example, 20 degrees to 30 degrees) with a coat rubber with respect to the tire circumferential direction. The cord is made of steel or organic fiber (polyester, rayon, nylon, etc.). Further, the overlapping belts 71 and 72 are arranged so that the cords intersect each other.

  The belt reinforcing layer 8 is configured as a cord reinforcing layer in the present embodiment. The belt reinforcing layer 8 is disposed on the outer side in the tire radial direction which is the outer periphery of the belt layer 7 and covers the belt layer 7 in the tire circumferential direction. The belt reinforcing layer 8 is formed by coating a plurality of cords (not shown) arranged in parallel in the tire width direction substantially parallel to the tire circumferential direction (including a range of ± 5 degrees) with a coat rubber. The cord is made of steel or organic fiber (polyester, rayon, nylon, etc.). The belt reinforcing layer 8 shown in FIG. 1 is disposed so as to cover the entire belt layer 7 and is disposed so as to cover the end of the belt layer 7 in the tire width direction. The configuration of the belt reinforcing layer 8 is not limited to the above, and is not clearly shown in the drawing. For example, the belt reinforcing layer 8 may be arranged so as to cover only the end portion of the belt layer 7 in the tire width direction. Further, although the configuration of the belt reinforcing layer 8 is not clearly shown in the drawing, for example, the belt reinforcing layer 8 is arranged so as to cover the entire belt layer 7 with a plurality of layers, or covers only the end in the tire width direction of the belt layer 7 with a plurality of layers. It may be arranged like this. The belt reinforcing layer 8 is provided by winding a strip-shaped strip material (for example, a width of 10 [mm]) in the tire circumferential direction. Note that the pneumatic tire 1 of the present embodiment includes a configuration in which the belt reinforcing layer 8 is not provided and the cord reinforcing layer includes only the belt layer 7.

  The inner liner layer 9 is the inner surface of the tire, that is, the inner peripheral surface of the carcass layer 6, and both end portions in the tire width direction reach the lower portions of the bead cores 51 of the pair of bead portions 5 and are formed in a toroidal shape in the tire circumferential direction. It is hung around and pasted. The inner liner layer 9 is for suppressing the permeation of air molecules to the outside of the tire.

  2 to 5 are enlarged views of main parts of the pneumatic tire according to the present embodiment.

  In the pneumatic tire 1 described above, as shown in FIGS. 1 to 5, the tread rubber of the tread portion 2 is composed of a cap tread rubber layer 2 </ b> A and an under tread rubber layer 2 </ b> B. The cap tread rubber layer 2 </ b> A is a portion that forms the surface of the tread portion 2 and contacts the road surface. Further, in the present embodiment, the cap tread rubber layer 2A is configured by providing at least two kinds of rubber compositions in the tire width direction. FIG. 1 shows a cap tread rubber layer 2A having a dual tread structure provided with two types of rubber compositions 2Aa and 2Ab.

  When the pneumatic tire 1 of the present embodiment is mounted on a vehicle (not shown), the direction with respect to the inner side and the outer side of the vehicle is specified in the tire width direction. The designation of the direction is not clearly shown in the figure, but is indicated by, for example, an index provided on the sidewall portion 4. Hereinafter, the side facing the inner side of the vehicle when mounted on the vehicle is referred to as the inner side of the vehicle, and the side facing the outer side of the vehicle is referred to as the outer side of the vehicle. In addition, designation | designated of a vehicle inner side and a vehicle outer side is not restricted to the case where it mounts | wears with a vehicle. For example, when the rim is assembled, the direction of the rim with respect to the inside and outside of the vehicle is determined in the tire width direction. For this reason, when the rim is assembled, the pneumatic tire 1 is designated with respect to the inner side (vehicle inner side) and the outer side (vehicle outer side) of the vehicle in the tire width direction. In the tread portion 2, the vehicle inner side means a range inside the vehicle with respect to the tire equator plane (tire equator line) CL when mounted on the vehicle, and the vehicle outer side means a tire equator when mounted on the vehicle. A range outside the vehicle from the surface (tire equator line) CL.

  The two different rubber compositions 2Aa and 2Ab of the cap tread rubber layer 2A have the breaking strength and breaking elongation of the rubber composition 2Aa on the outside of the vehicle, and the breaking strength and breaking elongation of the rubber composition 2Ab on the inside of the vehicle. Is set to a larger value. That is, a large amount of carbon black is blended as a filler of the rubber composition 2Aa on the outside of the vehicle so that the values of breaking strength, breaking elongation, and hardness are relatively large. Further, the rubber composition 2Ab on the inner side of the vehicle is disposed so as to reach the outer side in the tire width direction from the tire equatorial plane CL, and is provided in a wider range than the rubber composition 2Aa on the outer side of the vehicle. When the cap tread rubber layer 2A is composed of two different rubber compositions 2Aa and 2Ab as described above, both the steering stability on the dry road surface (dry road surface) and the steering stability on the wet road surface (wet road surface) can be achieved. Can do. That is, by setting the breaking strength and breaking elongation of the rubber composition 2Aa on the outside of the vehicle in the cap tread rubber layer 2A to a value larger than that of the rubber composition 2Ab on the inside of the vehicle, the breaking strength, breaking elongation on the outside of the vehicle, The value of hardness is relatively large and the handling stability on dry road surface is improved, and the value of breaking strength, breaking elongation and hardness are relatively small inside the vehicle, and the driving stability on wet road surface is relatively small. improves.

  The under tread rubber layer 2B is provided on the inner side in the tire radial direction of the cap tread rubber layer 2A and on the outer side in the tire radial direction of the belt reinforcing layer 8 and the belt layer 7 that are cord reinforcing layers.

  The main groove 22 and the lug groove 24 are formed in the cap tread rubber layer 2A. The main groove 22 is provided such that the boundary between the rubber compositions 2Aa and 2Ab of the cap tread rubber layer 2A is the groove bottom. Among the main grooves 22, the main groove 22 provided so that the boundary between the rubber compositions 2Aa and 2Ab of the cap tread rubber layer 2A is the groove bottom, and the conductive rubber layer 10 is provided on the groove surface. . The conductive rubber layer 10 has a groove surface portion 10a formed along the groove surface of the main groove 22 and a groove bottom of the main groove 22 at the boundary between the rubber compositions 2Aa and 2Ab of the cap tread rubber layer 2A. And a groove bottom extending portion 10b extending inward in the tire radial direction from the groove surface portion 10a. As shown in FIGS. 2 to 5, the groove bottom extending portion 10 b penetrates the undertread rubber layer 2 </ b> B and is in contact with the cord reinforcing layer.

  In FIG. 2, the groove bottom extending portion 10 b penetrates the belt reinforcing layer 8 and is in contact with the coat rubber of the belt layer 7 in the configuration having the belt reinforcing layer 8. In FIG. 3, the groove bottom extending portion 10 b is in contact with the coat rubber of the belt reinforcing layer 8 in the configuration having the belt reinforcing layer 8. In FIG. 4, the groove bottom extending portion 10 b is in contact with the coat rubber of the belt layer 7 in the configuration without the belt reinforcing layer 8.

  As described above, the pneumatic tire 1 of the present embodiment includes a cap tread rubber layer 2A having at least two kinds of rubber compositions 2Aa and 2Ab provided on the tread portion 2 in the tire width direction on the surface of the tread portion 2. An under tread rubber layer 2B provided on the inner side in the tire radial direction of the cap tread rubber layer 2A, and cord reinforcing layers 8 and 7 provided on the inner side in the tire radial direction of the under tread rubber layer 2B, and a cap In the pneumatic tire 1 in which the main groove 22 extending along the tire circumferential direction is formed so that the boundary between the rubber compositions 2Aa and 2Ab of the tread rubber layer 2A is the groove bottom, the groove surface of the main groove 22 is It extends from the groove surface portion 10a to the inner side in the tire radial direction at the groove bottom of the main groove 22 at the boundary between the covering groove surface portion 10a and the rubber compositions 2Aa and 2Ab of the cap tread rubber layer 2A. Comprising a conductive rubber layer 10 having a groove bottom extending portion 10b in contact with the cord reinforcing layer 8 and 7 through the under tread rubber layer 2B was.

  According to this pneumatic tire 1, since the boundary between the rubber compositions 2Aa and 2Ab of the cap tread rubber layer 2A is arranged at the groove bottom position of the main groove 22, the boundary does not contact the road surface. Abrasion, chipping and peeling can be prevented. Moreover, according to this pneumatic tire 1, the groove surface of the main groove 22 is covered with the groove surface portion 10 a, and the conductive rubber layer 10 in which the groove bottom extending portion 10 b is disposed at the boundary position is provided. Generation of cracks starting from the boundary between the rubber compositions 2Aa and 2Ab can be suppressed. Furthermore, according to this pneumatic tire 1, since the groove bottom extending part 10b penetrates the undertread rubber layer 2B and contacts the cord reinforcing layers 8 and 7, the electric resistance value can be reduced.

  In the pneumatic tire 1 of the present embodiment, the conductive rubber layer 10 preferably has a breaking strength of 15 MPa or more and a breaking elongation of 550% or more.

  According to the pneumatic tire 1, the effect of suppressing the occurrence of cracks starting from the boundaries between the rubber compositions 2Aa and 2Ab can be significantly obtained by the breaking strength and breaking elongation set in the conductive rubber layer 10. it can.

  The breaking strength and breaking elongation are measured according to JIS K6251. If the breaking strength is 15 MPa or more, it is possible to suppress the groove width from being widened by an external force applied to the tire during traveling of the vehicle. On the other hand, if the elongation at break is 550% or more, each rubber composition of the cap tread rubber layer 2A when the land portion 23 adjacent to the main groove 22 is greatly deformed by receiving a large lateral force or coming into contact with the road surface unevenness. The influence on the boundary between the objects 2Aa and 2Ab can be reduced.

In the pneumatic tire 1 of the present embodiment, the conductive rubber layer 10 preferably has an electric resistance value of 10 ⁶ Ω · cm or less.

  According to the pneumatic tire 1, the effect of reducing the electrical resistance value can be significantly obtained by the electrical resistance value set in the conductive rubber layer 10.

In the conductive rubber layer 10 having an electric resistance value of 10 ⁶ Ω · cm or less, for example, 40 parts by weight or more, preferably 45 to 70 parts by weight of carbon black is blended in 100 parts by weight of a diene rubber base material. Is generated. Moreover, in order to improve electroconductivity, conductive agents, such as an antistatic agent, a conductive plasticizer, and a metal salt, may be added, for example.

  In the pneumatic tire 1 of the present embodiment, the conductive rubber layer 10 preferably has a thickness in the tire meridian cross section of 0.5 mm or greater and 6.0 mm or less.

  The thickness of 0.5 mm or more and 6.0 mm or less is an average value of the thicknesses W1 and W2 of the groove surface portion 10a and the groove bottom extending portion 10b of the conductive rubber layer 10. According to the pneumatic tire 1, the conductive rubber layer 10 has a large effect of reducing electrical resistance if the thicknesses W1 and W2 in the tire meridional section are 0.5 mm or more, and conductive if the thickness is 6.0 mm or less. The increase in the volume of the conductive rubber layer 10 can ensure high-speed durability due to heat generation during vehicle travel.

  Further, in the pneumatic tire 1 of the present embodiment, the conductive rubber layer with respect to the hardness of each cap tread rubber layer 2A (rubber compositions 2Aa and 2Ab) on both sides in the tire width direction with the conductive rubber layer 10 as a boundary. The hardness difference of 10 is preferably ± 5 pt.

  According to this pneumatic tire 1, if the hardness difference of the conductive rubber layer 10 with respect to the cap tread rubber layer 2A is ± 5 pt, the peeling force between the cap tread rubber layer 2A and the conductive rubber layer 10 is increased. Since it can be suppressed to a small size, high-speed durability can be ensured.

  In the pneumatic tire 1 of the present embodiment, as shown in FIGS. 2 and 5, the conductive rubber layer 10 has a thickness W2 in the tire meridional section of the groove bottom extending portion 10b that is the thickness of the groove surface portion 10a. It is preferable that it is formed thicker than the length W1.

  According to the pneumatic tire 1, conductivity to the cord reinforcing layers 7 and 8 can be ensured.

  Further, in the pneumatic tire 1 of the present embodiment, as shown in FIG. 5, the conductive rubber layer 10 is formed such that the shape of the groove bottom extending portion 10 b in the tire meridian cross section gradually increases inward in the tire radial direction. It is preferable to form thickly.

  The shape in which the thickness is gradually increased toward the inner side in the tire radial direction has a trapezoidal shape as shown in FIG. 5, and although not explicitly shown in the figure, the middle toward the inner side in the tire radial direction is gradually caused by bending or bending. The thickness may be increased. According to the pneumatic tire 1, conductivity to the cord reinforcing layers 7 and 8 can be ensured.

  In this example, for a plurality of types of pneumatic tires having different conditions, the tire electrical resistance value, which is an electrical resistance reduction performance, high-speed steering stability (dry road), high-speed steering stability (wet road), presence or absence of a crack under the groove, A performance test on high-speed durability performance was performed (see FIG. 6).

  In this performance test, a pneumatic tire (test tire) having a tire size of 235 / 45R19 was assembled to a regular rim of 19 × 8 J and filled with a regular internal pressure (250 kPa).

  Here, the regular rim is “standard rim” defined by JATMA, “Design Rim” defined by TRA, or “Measuring Rim” defined by ETRTO. The normal internal pressure is “maximum air pressure” defined by JATMA, the maximum value described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “INFLATION PRESSURES” defined by ETRTO. The normal load is “maximum load capacity” defined by JATMA, the maximum value described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “LOAD CAPACITY” defined by ETRTO.

  The evaluation method of the tire electrical resistance value, which is the electrical resistance reduction performance, is to measure the electrical resistance value Ω of the resistance value between the tread surface and the rim by applying a voltage of 1000 V under the conditions of an air temperature of 23 ° C. and a humidity of 50% Is done. The electrical resistance value is measured in accordance with JATMA using a model HP4339A high resistance meter manufactured by Hured Packard with a pneumatic pressure of 200 kPa applied to each test tire and a load of 5.42 kN. The electric resistance value of the tire tread when 500 V was applied was measured. The results are also shown in Table 1. This evaluation shows that the smaller the numerical value, the better the discharge performance and the better the electrical resistance reduction performance.

  The method for evaluating high-speed steering stability (dry road and wet road) is as follows. The test tire is mounted on a test vehicle (5-door hatchback vehicle with a displacement of 3000 cc) and traveled at a speed of 60 km / h to 240 km / h. Steering stability was evaluated by sensory evaluation by a skilled driver for items of turning stability, rigidity, and steering at cornering. Then, based on this sensory evaluation, index evaluation using the conventional example as a reference (100) is performed. This evaluation shows that the higher the index, the better the high speed steering stability.

  The evaluation method for the presence or absence of sub-groove cracks is to visually check the presence or absence of cracks at the bottom of the main groove provided with a conductive rubber layer after running a test tire (a 5-door hatchback car with a displacement of 3000 cc) and running 30000 km. confirmed.

  The high-speed durability is evaluated by a test tire having an internal pressure increased by 120% of the specified internal pressure, dried and deteriorated for 5 days in an environment at a temperature of 80 ° C., set to the specified internal pressure, and a drum tester with a camber with a drum diameter of 1707 mm. Then, the vehicle starts running at a speed of 120 km / h and a load load of 5 kN, and the test is performed until the tire breaks while increasing the speed by 10 km / h every 24 hours, and the travel distance at the time of breakage is measured. Then, based on this measurement, index evaluation using the conventional example as a reference (100) is performed. This evaluation shows that the higher the index, the better the high-speed durability.

  In FIG. 6, the pneumatic tire of the conventional example is a cap tread rubber layer having a dual tread structure provided with two types of rubber compositions, and the boundary of each rubber composition of the cap tread rubber layer is the groove bottom. A main groove extending along the tire circumferential direction is formed, covers the groove surface of the main groove, and extends inward in the tire radial direction at the groove bottom of the main groove at the boundary of each rubber composition of the cap tread rubber layer. And a conductive rubber layer in contact with the undertread rubber layer.

On the other hand, in FIG. 6, the pneumatic tires of Examples 1 to 13 are cap tread rubber layers having a dual tread structure in which two types of rubber compositions are provided, and each of the rubber compositions of the cap tread rubber layers. A main groove extending along the tire circumferential direction is formed so that the boundary is a groove bottom, and the groove surface portion covering the groove surface of the main groove and the groove surface at the boundary of each rubber composition of the cap tread rubber layer And a conductive rubber layer having a groove bottom extending portion that extends inward in the tire radial direction of the groove bottom of the main groove and penetrates the undertread rubber layer and contacts the cord reinforcing layer. The pneumatic tire of Example 1 corresponds to the configuration shown in FIG. 4, the pneumatic tire of Example 2 corresponds to the configuration shown in FIG. 3, and Examples 3 to 13 have the configuration shown in FIG. Equivalent to. In Examples 4 to 13, the breaking strength of the conductive rubber layer is 15 MPa or more and the breaking elongation is 550% or more. In Examples 5 to 13, the electric resistance value of the conductive rubber layer is set. Is 10 ⁶ Ω · cm or less. In Examples 7 to 13, the thickness of the conductive rubber layer is 0.5 mm or more and 6.0 mm or less, and Examples 10 to 13 are conductive rubbers. The hardness difference of the conductive rubber layer is ± 5 pt with respect to the hardness of each of the undertread rubber layers on both sides in the tire width direction with the layer as a boundary. Examples 12 and 13 are the groove bottoms of the conductive rubber layers. In the thirteenth embodiment, the shape of the groove bottom extending portion is formed so as to gradually increase in thickness toward the inner side in the tire radial direction.

  As shown in the test results of FIG. 6, the pneumatic tires of Examples 1 to 13 are tire resistance values, high-speed driving stability (dry road), high-speed driving stability (wet road), which are electric resistance reduction performances. ), It can be seen that the presence or absence of cracks under the groove and high-speed durability are improved.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 2A Cap tread rubber layer 2Aa, 2Ab Rubber composition 2B Under tread rubber layer 7 Belt layer (cord reinforcement layer)
8 Belt reinforcement layer (cord reinforcement layer)
10 conductive rubber layer 10a groove surface portion 10b groove bottom extending portion

Claims (7)

A cap tread rubber layer having at least two kinds of rubber compositions provided in the tire width direction on the surface of the tread portion on the tread portion, and an under tread rubber provided on the inner side in the tire radial direction of the cap tread rubber layer And a cord reinforcing layer provided on the inner side in the tire radial direction of the under tread rubber layer, and along the tire circumferential direction so that a boundary of each rubber composition of the cap tread rubber layer is a groove bottom In the pneumatic tire formed with the main groove extending,
The under tread rubber extends from the groove surface portion to the inside in the tire radial direction of the groove bottom of the main groove at the boundary between the groove surface portion covering the groove surface of the main groove and each rubber composition of the cap tread rubber layer. A pneumatic tire comprising a conductive rubber layer having a groove bottom extending portion that penetrates the layer and contacts the cord reinforcing layer.   The pneumatic tire according to claim 1, wherein the conductive rubber layer has a breaking strength of 15 MPa or more and a breaking elongation of 550% or more. The pneumatic tire according to claim 1 or 2, wherein the conductive rubber layer has an electric resistance value of 10 ⁶ Ω · cm or less.   The pneumatic tire according to any one of claims 1 to 3, wherein the conductive rubber layer has a thickness in a tire meridian cross section of not less than 0.5 mm and not more than 6.0 mm.   The hardness difference of the said conductive rubber layer is +/- 5pt with respect to each hardness of each cap tread rubber layer of the tire width direction both sides with the said conductive rubber layer as a boundary, The any one of Claims 1-4 characterized by the above-mentioned. A pneumatic tire according to any one of the above.   6. The conductive rubber layer according to claim 1, wherein a thickness of the groove bottom extension portion in a tire meridian cross section is formed to be thicker than a thickness of the groove surface portion. Pneumatic tire described in one.   7. The conductive rubber layer according to claim 1, wherein the shape of the groove bottom extending portion in the tire meridian cross section is formed to gradually increase in thickness toward the inner side in the tire radial direction. Pneumatic tire described in one.

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